EUVD-2026-21061
CVSS Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
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3Description
Apollo MCP Server is a Model Context Protocol server that exposes GraphQL operations as MCP tools. Prior to version 1.7.0, the Apollo MCP Server did not validate the Host header on incoming HTTP requests when using StreamableHTTP transport. In configurations where an HTTP-based MCP server is run on localhost without additional authentication or network-level controls, this could potentially allow a malicious website-visited by a user running the server locally-to use DNS rebinding techniques to bypass same-origin policy restrictions and issue requests to the local MCP server. If successfully exploited, this could allow an attacker to invoke tools or access resources exposed by the MCP server on behalf of the local user. This issue is limited to HTTP-based transport modes (StreamableHTTP). It does not affect servers using stdio transport. The practical risk is further reduced in deployments that use authentication, network-level access controls, or are not bound to localhost. This vulnerability is fixed in 1.7.0.
Analysis
Apollo MCP Server versions prior to 1.7.0 fail to validate HTTP Host headers on StreamableHTTP transport, allowing unauthenticated remote attackers with user interaction to bypass same-origin policy via DNS rebinding attacks and invoke GraphQL tools or access resources on behalf of a local user. The vulnerability is limited to HTTP-based deployments without network-level controls and does not affect stdio transport configurations. …
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